This invention relates to direct injected internal combustion engines and more particularly to an improved operational method and apparatus for a two stroke direct injected internal combustion engine.
In the interest of continuing to improve the performance of internal combustion engines both in terms of output as well as exhaust emission control and fuel economy, direct cylinder injection is quite favorable. However, there are some instances when direct injection may not operate as efficiently or as good as forms of manifold injection. Manifold injection being injection of the fuel into the intake system upstream of the combustion chamber. In addition, there are certain problems inherent in the use of direct injection which has resulted in reduced application of this principle.
One difficulty with direct injected engines is that the fuel injector is generally positioned so that it will be exposed to the combustion conditions in the combustion chamber, particularly at the initial time of firing and during initial, rapid flame propagation. This necessitates the use of very expensive components and also still gives rise to the possibility that the fuel injector may become contaminated.
It is, therefore, a principle object to this invention to provide an improved fuel injector arrangement for an internal combustion engine wherein direct injection can be enjoyed, but wherein the injector is protected from the initial phase of combustion thus permitting the use of lower cost and longer life injectors.
When direct injection is employed, it is also necessary that the injector be capable of injecting fuel at quite high pressures. This is because the injector is exposed in the combustion chamber and at least part of the injection cycle takes place when the mixture in the combustion chamber is relatively highly compressed. The use of high pressure injection systems, however, presents certain difficulties.
First, when high pressure injection is employed higher pressure pumps must be provided and regulation of pressure becomes more critical. Furthermore, the injection penetration can, at times, become greater than desired and result in deposition of more fuel than desired within the surfaces of the combustion chamber. This can result in plug fouling and other undesirable conditions.
It is, therefore, a still further object of this invention to provide an improved direct injected internal combustion engine wherein the injection can be controlled so as to avoid the necessity of spraying into high pressure areas and/or employing high pressure under all injection conditions.
Many of the problems which were noted previously and which will be discussed later are even more acute when the injection system is employed with a two cycle engine. With two cycle engines, the time at which direct cylinder injection can occur is quite limited due to the fact that the engine fires every revolution of the crankshaft rather than every other revolution as with a four cycle engine. This further exacerbates the problems already noted.
It is, therefore, a still further object of this invention to provide an improved injection system and method for a two cycle engine which permits direct cylinder injection without necessitating high pressures.
One particularly acute problem in connection with direct injection engines is during starting and particularly cold starting. Because of the low temperature of the engine and the fact that it is cranked relatively slowly during starting, it is generally necessary to provide a richer than normal mixture so as to ensure the existence of a stoichiometric fuel air mixture at the time ignition occurs.
If high pressure systems are employed, it takes time for the system to develop the high pressure, particularly when high pressure engine driven pumps are employed. Thus, the injector may not develop adequate pressure to sufficiently vaporize the fuel during starting.
It is, therefore, a still further object to this invention to provide an improved arrangement for starting a fuel injected engine wherein vaporization of the fuel can be improved during starting and high pressure generation is not required.
It has been previously noted that the problems attendant with direct injection are more acute in many instances with two cycle engines than four cycle engines. The starting conditions and also high speed high load operating conditions are such that it may not be possible to inject all of the fuel required for combustion under some running conditions if only direct injection is employed.
It is, therefore, a still further object to this invention to provide an improved injection systems for an engine wherein fuel may be injected directly into the combustion chamber under some running conditions and into the induction tract under other running conditions.
Although the goals mentioned in the preceding paragraph are obtainable if the system is provided with two fuel injectors, one directly injecting into the combustion chamber and the other injecting into the induction system, this further complicates the system. This is particularly true if the direct injection system need be a high pressure system and the manifold injection system is a low pressure system. This provides difficulties in having two different pressure regulating systems and also two different supply systems, one for each injector.
It is, therefore, a still further object of this invention to provide an improved arrangement for utilizing a single injector which can be operated in such a way so as to inject fuel into the induction system under some running conditions and directly into the combustion chamber under other running conditions.
With two cycle engines and those having only direct cylinder injection, at times the heat in the combustion chamber and particularly at the head of the piston can be too high. During normal crankcase compression engine operation and when utilizing fuel introduction into the crankcase or induction system that feeds the crankcase, there is some cooling of the underside of the piston due to fuel evaporation.
If only direct cylinder injection is employed, this cooling may be lost and thus it is a still further object to this invention to provide an improved injection system wherein fuel can be selectively injected by a single injector directly into the combustion chamber and/or into the induction system depending upon specific running conditions.